Gland Steam Sealing System for Steam turbine

Summary

The script explains the process of sealing a steam turbine's shaft to prevent leaks and air ingress. It details how labyrinth seals, consisting of sharp, thin edges, minimize steam leakage by creating a tortuous path. The gland sealing system uses steam from the cold reheat line for shaft sealing during turbine operation. Steam leakages are collected and condensed via the gland steam condenser system. The process ensures efficient steam flow through high-pressure, intermediate-pressure, and low-pressure stages, preventing unwanted steam loss and ensuring optimal turbine performance.

Takeaways

• 🛠️ The labyrinth packing set plays a key role in reducing leakages along the turbine shaft and shell penetrations.
• 🌬️ Steam sealing is critical before steam enters the turbine for rolling, and leakoff steam is required to prevent air ingress into shaft glands.
• 🔥 Gland sealing steam is supplied from the main steam supply, specifically from the cold reheat line via the HP bypass valve.
• 🚿 A condensate spray is used to desuperheat the gland sealing steam for the low-pressure (LP) end of the turbine to reach an acceptable temperature.
• 🔩 Low-pressure packing is located at the condenser end of the turbine, near the number one journal bearing.
• 🌀 Labyrinth seals, with sharp raised edges, prevent steam leakage along the turbine shaft by creating a tortuous path for steam to travel.
• ⚙️ Intermediate stage packing is positioned at the reheat steam inlet, acting as a seal between the high-pressure and intermediate-pressure sections of the turbine.
• 🔧 High-pressure packing is located on the generator end of the turbine, ensuring steam does not leak from the high-pressure turbine section.
• 🌡️ Bleed-off steam from various valves is routed to the gland steam condenser, where it is condensed by cooling water and returned to the main condenser.
• 💨 The gland steam system manages leakoff steam from multiple steam valves, including main and reheat steam control valves, preventing excess steam from escaping.

Q & A

What is the purpose of the labyrinth packing set in a steam turbine?

The labyrinth packing set is designed to reduce leakages along the turbine shaft and shaft penetrations. It consists of steam seal areas that prevent air in-leakage and control steam leakage along the turbine shaft.

Why is a source of steam needed to seal turbine shaft penetrations during startup?

During startup, there is no leakoff steam available to seal the shaft glands. A source of steam is needed to prevent air from leaking into the turbine by sealing the shaft penetrations before steam is fully admitted for turbine rolling.

How is gland sealing steam supplied to the turbine?

Gland sealing steam is supplied from the cold reheat line by way of the high-pressure (HP) bypass valve. As the cold reheat steam line becomes pressurized, some steam is taken off to provide shaft sealing steam.

Why is the gland sealing steam to the low-pressure (LP) gland desuperheated?

The gland sealing steam to the LP gland is desuperheated to reduce its temperature to an acceptable level for use at the LP end of the turbine, ensuring it doesn’t damage the components.

Where is the low-pressure packing located on the steam turbine?

The low-pressure packing is located on the condenser end of the turbine rotor, near the number one journal bearing.

What function do the labyrinth seals perform on a steam turbine?

Labyrinth seals prevent steam leakage by creating a tortuous path through sharp, thin, raised edges that protrude toward the shaft and fit into machined ridges on the turbine shaft. This design slows or stops steam leakage along the shaft.

Where is the intermediate stage packing located, and what does it seal?

The intermediate stage packing is located at the reheat steam inlet and seals the interface between the high-pressure and intermediate-pressure sections of the turbine.

What is the role of the high-pressure packing in the steam turbine?

The high-pressure packing is located on the generator end of the turbine rotor. It helps prevent steam leakage as the main steam exits the high-pressure turbine.

What happens to the steam that bleeds through the packing in a steam turbine?

Some steam bleeds through the packing and is routed to pipes on the bottom of the turbine casing. This bleed-off steam goes to the gland steam condenser, where it is condensed and transferred to the main condenser.

What is the purpose of the gland steam condenser in the system?

The gland steam condenser is designed to condense the leakoff steam from the packing glands and the steam valve stems. The condensed steam is then transferred to the main condenser.